Preparation Of Soluble Dietary Fiber From Soybean Residues By Extrusion-enzymatic Technology And Its Properties

As main by-product of soybean processing, soybean residues whose main ingredients is dietary fiber is an ideal source of dietary fiber due to its low price. Soybean residues soluble dietary fiber not only has physico-chemical and functional properties of dietary fiber, but also has higher physiological activity comparing with insoluble dietary fiber.Furthermore,soybean soluble dietary fiber products has good healthyfunction and stability. Therefore, the development and utilization of soybean residues have great development prospects.In this paper, soybean residues were used as raw material. The extrusion-enzymatic extraction process of soybean residues soluble dietary fiber(SDF)was optimized. Original soybean residues soluble dietary fiber(SDF1), enzymatic hydrolysis soybean residues soluble dietary fiber(SDF2),extrudedsoybean residues soluble dietary fiber(SDF3) and extrusion-enzymaticsoybean residues soluble dietary fiber(SDF4)were extracted and theirproperties and structure were investigated. The results are as follows:(1)The preparation of soluble dietary fiber of soybean residuesThe optimum condition of extrusion-enzymatic preparation soybean residues SDF was obtained through single factor and orthogonal experiment. Under the optimal condition:extrusiontemperature of 150℃, feeding moisture of 55%, screw rotating speed of 160 r/min,material-water ratio of 1︰20, enzyme volume of 106 U/g soybean residue, enzymatic temperature of 55℃ and hydrolysis 2h. The yield of SDF was up to(19.87±0.27)% through this progress. SDF extracted directly from the raw soybean residues, the extraction rate is(2.10 ± 0.11)%; SDF extractedby cellulase under the same solution conditions for processing, the extraction rate was(6.28 ± 0.06) %. In the same conditions of extrusion processing of soybean residues, without cellulase processing, the extraction rate was(7.24±0.16) %.Extrusion- enzymatic preparation of soluble dietary fiber from soybean residues can improve the extraction rate, whichwas morethan 9 times to original soybean residues extraction, more than twice to enzymatic preparation and more than 2.7 times to squeezing preparation.(2)The physico-chemical and functional properties of four kinds of soluble dietary fiber were studied.The transparency of SDF2 and SDF4 were obviously higher than SDF1 and SDF3, whichindicated that the molecular weight of soybean soluble dietary fiber acquired by enzymatica preparation was small. As a result of that, the transparency increased. Compared with SDF1~3, the viscosity of SDF4 was the lowest, while both cation exchange capacity and theadsorption on cholesterol of SDF4 were the biggest. SDF4 had a greater binding force on glucose during dialysising. What’s more, the adsorption on glucose of it wasthe biggest with(186.47±11.64) mg/g.The ability of scavenge ABTS+ of SDF4 was 0.8060 + 0.0275mmol/g.There is no significant difference of iron reduction ability between SDF3 and SDF4(p<0.05), which is obviously bigger than SDF1 and SDF2. It is illustrated that the iron reduction ability of soluble fiber increased because of extrusion. The biggest scavenging ·OH ability of soluble dietary fiber was found in SDF4, followed by SDF2, SDF3 and SDF1. The four kinds of SDF could promote the proliferation of Lactobacillus. The proliferation of Lactobacillus in different concentration of SDF stroma in0~24 h was greater than that in control condition.(3)The molecular weight, particle size, particle state, functional group composition and aggregation state of four kinds of soluble dietary fiber were studied.Molecular weight explained that, in contrast to SDF1, the molecular weight distribution of SDF2~4 were wider. The constituent content of small molecule increased. Among them, the molecular weight of SDF4 was the smallest. The volume mean diameter D[4,3] of SDF1, SDF2,SDF3 and SDF4 was(107.988±4.368),(44.325±7.091),(92.121±4.578) and(39.311±0.657) μm respectively. The particle size of SDF4 was the smallest, SDF1 is the biggest. According to the scanning electron microscope, SDF2 and SDF4 were similar in surface which is small particle and loose structure, whereas SDF1 and SDF3 were relatively smooth, which suggested that SDF2 and SDF4 by enzymolysis may have great solubility and adsorption capacity. Infrared spectrum showed that all of SDF possessed polysaccharides characteristics and the difference is not obvious.Based on X-ray diffraction analysis, SDF showed distinct peaks appeared at 2θ=22°~23° and were with a typical crystalline crystalline form of cellulose I.